[FFmpeg-devel] [PATCH 2/4] opus: Fix arithmetic overflows (per RFC8251)

[Andrew D'Addesio]

The relevant sections from the RFC are:

Sec.6. Integer Wrap-Around in Inverse Gain Computation
    32-bit integer overflow in Levinson recursion. Affects
    silk_is_lpc_stable().

Sec.8. Cap on Band Energy
    NaN due to large log-energy value. Affects celt_denormalize().

Signed-off-by: Andrew D'Addesio <modchipv12 at gmail.com>
---
 libavcodec/opus_celt.c |  3 ++-
 libavcodec/opus_silk.c | 11 +++++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/libavcodec/opus_celt.c b/libavcodec/opus_celt.c
index 84d4847..ff56041 100644
--- a/libavcodec/opus_celt.c
+++ b/libavcodec/opus_celt.c
@@ -481,7 +481,8 @@ static void celt_denormalize(CeltFrame *f, CeltBlock *block, float *data)
 
     for (i = f->start_band; i < f->end_band; i++) {
         float *dst = data + (ff_celt_freq_bands[i] << f->size);
-        float norm = exp2f(block->energy[i] + ff_celt_mean_energy[i]);
+        float log_norm = block->energy[i] + ff_celt_mean_energy[i];
+        float norm = exp2f(FFMIN(log_norm, 32.0f));
 
         for (j = 0; j < ff_celt_freq_range[i] << f->size; j++)
             dst[j] *= norm;
diff --git a/libavcodec/opus_silk.c b/libavcodec/opus_silk.c
index 3c9c849..344333c 100644
--- a/libavcodec/opus_silk.c
+++ b/libavcodec/opus_silk.c
@@ -185,8 +185,15 @@ static inline int silk_is_lpc_stable(const int16_t lpc[16], int order)
         row = lpc32[k & 1];
 
         for (j = 0; j < k; j++) {
-            int x = prevrow[j] - ROUND_MULL(prevrow[k - j - 1], rc, 31);
-            row[j] = ROUND_MULL(x, gain, fbits);
+            int x = av_sat_sub32(prevrow[j], ROUND_MULL(prevrow[k - j - 1], rc, 31));
+            int64_t tmp = ROUND_MULL(x, gain, fbits);
+
+            /* per RFC 8251 section 6, if this calculation overflows, the filter
+               is considered unstable. */
+            if (tmp < INT32_MIN || tmp > INT32_MAX)
+                return 0;
+
+            row[j] = (int32_t)tmp;
         }
     }
 }
-- 
2.15.1.windows.2